diff --git a/lib/usb_cdcacm.c b/lib/usb_cdcacm.c
index 7d25abc..95c1874 100644
--- a/lib/usb_cdcacm.c
+++ b/lib/usb_cdcacm.c
@@ -262,13 +262,16 @@ static void usb_disconnect(void)
 	// enable USB D+ pull-up
 	rcc_periph_clock_enable(RCC_GPIOB);
 	gpio_set_mode(GPIOB, GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, GPIO6);
-	gpio_set(GPIOB, GPIO6);
+	gpio_clear(GPIOB, GPIO6);
 #endif
 	// pull USB D+ low for a short while
 	rcc_periph_clock_enable(RCC_GPIOA);
 	gpio_set_mode(GPIOA, GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, GPIO12);
 	gpio_clear(GPIOA, GPIO12);
-	sleep_ms(50); // USB disconnected must be at least 10 ms long, at most 100 ms
+	// USB disconnected must be at least 10 ms long, at most 100 ms
+	for (uint32_t i = 0; i < 0x2000; i++) {
+		__asm__("nop");
+	}
 }
 
 /** DFU detach (disconnect USB and perform core reset)
diff --git a/lib/usb_dfu.c b/lib/usb_dfu.c
index eab0ec1..1df306a 100644
--- a/lib/usb_dfu.c
+++ b/lib/usb_dfu.c
@@ -143,13 +143,16 @@ static void usb_disconnect(void)
 	// enable USB D+ pull-up
 	rcc_periph_clock_enable(RCC_GPIOB);
 	gpio_set_mode(GPIOB, GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, GPIO6);
-	gpio_set(GPIOB, GPIO6);
+	gpio_clear(GPIOB, GPIO6);
 #endif
 	// pull USB D+ low for a short while
 	rcc_periph_clock_enable(RCC_GPIOA);
 	gpio_set_mode(GPIOA, GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, GPIO12);
 	gpio_clear(GPIOA, GPIO12);
-	sleep_ms(50); // USB disconnected must be at least 10 ms long, at most 100 ms
+	// USB disconnected must be at least 10 ms long, at most 100 ms
+	for (uint32_t i = 0; i < 0x2000; i++) {
+		__asm__("nop");
+	}
 }
 
 /** flash downloaded data block